The purpose of this work is to study the factors regulating and controlling the sudden switch from 2,3-diphosphoglycerate (2,3-DPG) as the major organic phosphate of the chick embryo erythrocyte just before hatching to inositol pentaphosphate (IPP) as the major organic phosphate just after hatching. We have previously suggested that this sudden switch in distribution of intraerythrocytic phosphates is controlled by the abrupt changes in environmental oxygen and carbon dioxide tension. We want to establish the pathway of synthesis and degradation of 2,3-DPG in the erythrocytes of the chick embryo and chick, determine the similarity of this enzyme system (PGA cycle) to that of man, determine whether the enzyme activities of the PGA cycle are controlled by environmental O2 and CO2 tensions and whether this control is translatable to in vitro conditions, and determine the fate of 2,3-DPG in the chick erythrocytes. We will incubate eggs in various environments of O2 and CO2 and allow the chicks to hatch in various environments of O2 and CO2 balanced with N2. We will measure packed cell volumes, hemoglobin concentration, perform hemoglobin electrophoresis, determine 2,3-DPG levels of the erythrocytes, whole blood oxygen affinity, and PGA cycle enzyme activities of the erythrocytes. This work should provide information about the regulation of 2,3-DPG synthesis of degradation and whether regulation of organic phosphates is related in anyway to erythrocyte composition of hemoglobin.